Semester 1 Review 2023 IB Biology

What is the difference between eukaryotic and prokaryotic cells?

Eukaryotic and prokaryotic cells differ fundamentally in structure and organization. Prokaryotic cells, as seen in bacteria and archaea, lack a true nucleus and membrane-bound organelles, while eukaryotic cells, found in plants, animals, fungi, and protists, have a defined nucleus and various organelles. Prokaryotic cells are smaller, less complex, and divide through binary fission, whereas eukaryotic cells are larger, more complex, and divide through mitosis or meiosis. These distinctions highlight the essential disparities in their evolutionary paths, influencing their cellular characteristics.

Onion (Allium cepa) epidermis was placed in pure water and observed with a light microscope using high magnification.

What would happen to these cells if they were transferred to a hypertonic solution?

If onion (Allium cepa) epidermal cells, initially placed in pure water, are transferred to a hypertonic solution, the cells will likely undergo plasmolysis. Plasmolysis is a process where water leaves the cell due to a higher concentration of solutes outside the cell.

What cell component is found in eukaryotic cells but not in prokaryotic cells?

A true nucleus and membrane-bound organelles.

The diagram shows the structure of a cell in the pancreas that secretes digestive enzymes.

(a) Explain how the pancreas cell carries out its function, with reference to three organelles visible in the diagram.

(b) The pancreas secretes lipase into the small intestine.

(b.i) Outline the function of lipase

(b.ii) State one other enzyme secreted by the pancreas.

(a) (1) Endoplasmic Reticulum (ER): The rough endoplasmic reticulum (RER), depicted as ribosome-studded structures in the diagram, is responsible for the synthesis of proteins, including digestive enzymes. In this pancreas cell, it plays a crucial role in manufacturing the enzymes that will later be secreted.

(2) Golgi Apparatus: The Golgi apparatus, shown as flattened sacs in the diagram, is involved in modifying, processing, and packaging proteins synthesized in the ER. In the context of the pancreas cell, the Golgi apparatus processes the newly synthesized digestive enzymes, modifying them as necessary, and then packages them into vesicles for secretion.

(3) Vesicles: These vesicles, often derived from the Golgi apparatus, contain the processed and packaged digestive enzymes. They move towards the cell membrane, fuse with it, and release their contents (enzymes) into the extracellular space. This process is called exocytosis. In the pancreas, digestive enzymes are secreted into the pancreatic ducts, eventually reaching the small intestine to aid in digestion.

(b.i) Lipase is an enzyme that catalyzes the breakdown of lipids (fats) into fatty acids and glycerol. In the context of digestion, pancreatic lipase is essential for the digestion and absorption of dietary fats in the small intestine. It breaks down triglycerides into smaller molecules, facilitating their absorption by the intestinal lining.

(b.ii) Amylase: The pancreas secretes amylase, an enzyme that catalyzes the breakdown of complex carbohydrates (starches) into simpler sugars like maltose. Amylase plays a crucial role in the digestion of carbohydrates in the small intestine.

The diagram shows a prokaryotic cell.

What are the structures labelled Y and Z?

Z: 70S Ribosome

Y: Nucleoid

The diagram refers to questions 2 and 3. It shows a heterotrophic, unicellular, freshwater organism that has been placed in distilled water. The short arrows show movement of water and the long arrows show a sequence of steps.

What life function is illustrated?

Osmoregulation - the biological process by which organisms control the concentration of water and solutes within their cells in response to changes in the surrounding environment

More than 90 % of cellular cholesterol is located in the cell's plasma membrane. What is the main role of cholesterol in the plasma membranes of mammalian cells?

Cholesterol is important for the cell membrane in mammals because it keeps the membrane flexible, helps it stay strong, and controls what can pass through. These jobs are crucial to make sure the cell membrane works well and stays intact.

(a) Outline the stages in the production of mRNA by transcription.

(b) Describe the functions of proteins in cell membranes.

(c) Explain how natural selection can lead to speciation.

(a) RNA polymerase binds to the DNA at the promoter region. RNA polymerase moves along the DNA template strand, synthesizing mRNA by adding complementary RNA nucleotides. Transcription stops when RNA polymerase reaches the terminator sequence, and the newly formed mRNA molecule is released.

(b) Transport proteins facilitate the movement of ions and molecules across the cell membrane by acting as channels or carriers, maintaining the cell's internal environment. Receptor proteins, functioning as antennas, bind to specific signaling molecules, triggering cellular responses and conveying external signals into the cell's interior. Recognition proteins, integral in immune responses, identify self and non-self cells, crucial for preserving the body's integrity. Enzymatic proteins catalyze specific chemical reactions at the cell membrane, participating in processes like signal transduction, cell adhesion, and substance breakdown. Structural proteins, including integral membrane proteins, provide support and stability to the cell membrane, contributing to its overall shape and resilience against mechanical stress.

(c) Natural selection acts on genetic variation, favoring traits that enhance survival and reproduction. Isolation of populations allows for the accumulation of genetic differences, leading to reproductive isolation and the eventual formation of distinct species through speciation.

The diagram shows protein channels involved in the passive movement of a substance into the cell across the cell membrane.

What describes this movement?

Facilitated diffusion - a passive process that relies on the assistance of specific channel proteins or carrier proteins to allow the movement of substances, such as ions or polar molecules, across the membrane along their concentration gradient (from an area of higher concentration to an area of lower concentration). This process does not require energy input and is considered a form of passive transport.

What is evidence for the endosymbiotic theory?

the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote)

In an experiment on osmosis, red blood cells were immersed in a salt solution for two hours. The micrographs show the appearance of these cells before and after immersion in the salt solution.

What explains the observed changes?

After immersion in the salt solution, the red blood cells appear shriveled. The concentration of the salt solution is higher than that inside the red blood cells. In this hypertonic solution, water would move out of the cells, causing them to shrink.

The diagrams represent cells with the same concentration of dissolved substances in their cytoplasm. If all the cells were placed in the same hypertonic sucrose solution, which cell would show the greatest rate of change in the concentration of its cytoplasm?

5x20x20 (c)

Which cell component arose first during the formation of the earliest cells?

Cell Membrane (Plasma Membrane): It is often considered one of the earliest cellular components to evolve. The cell membrane is crucial for separating the internal environment of the cell from the external surroundings and controlling the passage of substances in and out of the cell.

Ribonucleic Acid (RNA): RNA is believed to have played a fundamental role in early cellular processes. Some hypotheses suggest that RNA may have preceded DNA as the genetic material in the earliest cells, serving both as a carrier of genetic information and as a catalyst in early metabolic reactions.

What would show that a person has developed metastatic cancer?

The detection of tumors in multiple organs. This is in contrast to a localized cancer that is confined to a specific organ or tissue.

In the micrograph, which letter points to a cell in anaphase?

B

(a) State one disaccharide and the two monomers from which it can be synthesized.

Disaccharide:

1: Sucrose

Monomers:

1: Glucose

2: Fructose

(b) Discuss the roles of the enzymes secreted by the pancreas during digestion.

Amylase: Secreted by the pancreas and salivary glands, amylase breaks down complex carbohydrates (starches) into simpler sugars like maltose.

Lipase: Acts on fats (lipids) and breaks them down into fatty acids and glycerol. This enzyme is crucial for lipid digestion and absorption.

Proteases (Trypsin and Chymotrypsin): These enzymes break down proteins into smaller peptides and amino acids. They are essential for protein digestion.

(c) Compare and contrast cis-fatty acids and trans-fatty acids.

Cis-fatty acids have a bent shape, while trans-fatty acids have a straighter shape. Cis-fatty acids are commonly found in natural sources, whereas trans-fatty acids are often produced through industrial processes. Cis-fatty acids are generally considered healthier, while high intake of trans-fatty acids is associated with health risks.

The anticodons of three tRNAs and the amino acids they carry are shown in the table.

tRNA anticodon:

GCA

AAU

CAG

Amino acid:

Arginine

Leucine

Valine

Which base sequence of an mRNA molecule would code for an arginine-leucine-valine tripeptide?

CGU-UUA-GUC

(a) Explain the role of hydrogen ions used in photosynthesis.

Hydrogen ions (protons) play a crucial role in the process of photosynthesis, particularly during the light-dependent reactions that occur in the thylakoid membrane of the chloroplast. In the thylakoid membrane, light energy is absorbed by chlorophyll, leading to the excitation of electrons. These excited electrons are then passed through a series of protein complexes known as the electron transport chain (ETC).

(b) Describe how the structure of the chloroplast is adapted to its function in photosynthesis.

The chloroplast's structure is adapted for photosynthesis through features such as a double membrane, thylakoid membrane system with grana for efficient light absorption, a stroma containing enzymes for the Calvin cycle, and the presence of chlorophyll pigments embedded in the thylakoid membrane.

(c) The enzyme Rubisco is used in carbon fixation during photosynthesis. Identify four other examples of proteins that illustrate the wide range of functions of this group of biochemicals in living organisms.

Hemoglobin: Hemoglobin is a protein responsible for oxygen transport in the blood. It binds to oxygen in the lungs and releases it in tissues where it is needed.

Insulin: Insulin is a protein hormone that regulates blood glucose levels by facilitating the uptake of glucose by cells, particularly in the liver and muscles.

Collagen: Collagen is a structural protein found in connective tissues, providing strength and support to various body structures such as skin, bones, tendons, and ligaments.

Antibodies (Immunoglobulins): Antibodies are proteins involved in the immune system's defense against pathogens. They recognize and neutralize foreign substances like bacteria and viruses.

Genome and proteome (relationship)

A genome is the complete and unique DNA content. A proteome is the unique set of proteins which is coded by the genome.

A molecule of DNA is found to contain 200 guanine bases, representing 25 % of the total number of bases. How many phosphate groups does this molecule of DNA contain?

800

What is a function of the enzyme helicase?

Helicase is an enzyme that unwinds and separates the DNA strands by breaking the hydrogen bonds during processes like DNA replication, repair, and transcription.

The hydrolysis of a pure sample of an organic molecule produces a pentose sugar, thymine, guanine and cytosine. What other substances could be expected to be present in the hydrolyzed sample?

In addition to thymine, guanine, cytosine, and a pentose sugar, the hydrolysis of the organic molecule likely produces phosphate groups and deoxyribose, indicating DNA composition.

What is common to RNA and DNA?

RNA and DNA share common features such as nucleotides, a phosphate-sugar backbone, nitrogenous bases (adenine, guanine, and cytosine), and the use of complementary base pairing for genetic information, but they differ in terms of the sugar (ribose in RNA and deoxyribose in DNA) and the presence of thymine in DNA or uracil in RNA.

What is a consequence of anaerobic cell respiration in muscles?

The consequence of anaerobic cell respiration in muscles is the production of lactic acid, leading to muscle fatigue, decreased pH, and a temporary but rapid source of energy during oxygen-limited conditions.

Which equation represents a process in yeast that causes bread to rise?

C6H12O6 (aq) ————> 2C2H5OH (aq) + 2CO2(g) + 2ATP

What is a difference between aerobic respiration and anaerobic respiration in yeast?

A difference between aerobic and anaerobic respiration in yeast is the use of oxygen as the terminal electron acceptor in aerobic respiration, leading to the production of carbon dioxide and water, while anaerobic respiration produces ethanol and carbon dioxide without involving the electron transport chain.

Which compound is a waste product of anaerobic respiration in humans?

Lactic acid

Cell theory

Cells are the basic unit of life. All living things are made up of cells. Cells are made by pre-existing cells.

Two functions of life

Metabolism: The set of chemical reactions that occur within a living organism to maintain life, including energy production, nutrient utilization, and waste elimination.

Reproduction: The process by which living organisms produce offspring, ensuring the continuity of their species.

Three characteristics of eukaryotic homologous chromosomes.

Similar Size: Homologous chromosomes are of the same length and carry genes controlling the same traits, although they may have different alleles.

Similar Centromere Position: The centromere, the point where chromatids are joined, is located at the same relative position on homologous chromosomes.

Same Genes, Different Alleles: Homologous chromosomes carry the same genes in the same order, but they may have different alleles, contributing to genetic diversity.

Compare and contrast anaerobic cell respiration in yeasts and in humans.

Require oxygen

- Yeast: no

- Humans: yes

Produce ethanol and CO2

- Yeast: yes

- Humans: no

Produce lactate

- Yeast: no

- Humans: yes

What are final products of photosynthesis and of aerobic respiration?

CO2 + H2O + ATP

Which process causes ADP to change to ATP?

Phosphorylation - occurs during cellular respiration, more specifically in the electron transport chain.

If a plant is exposed to light, which colour of light would lead to the lowest rate of oxygen release by a green plant?

Green light.